1. Field of the Invention
The present invention relates to an ABA tri-block copolymer. More particularly, the present invention relates to an ABA tri-block copolymer between a polyvinyl ether having an alicyclic structure in its side chain and a polyvinyl ether having an aliphatic structure in its side chain. The ABA tri-block copolymer is utilized as, for example, a novel thermoplastic elastomer.
2. Description of the Prior Art
Thermoplastic resins which are a polymer derived from a compound having a polymerizable functional group, such as, for example, a styrene, a (meth)acrylate, an olefin, a polyurethane, a vinyl chloride or the like, are being used in a wide variety of applications such as various molded materials, adhesive, coating material and the like. In particular, rubbery elastomers (thermoplastic elastomers) derived from the above monomers are in use for various purposes such as adhesive, building sealant, modifier and the like.
Meanwhile, polymers derived from a vinyl ether having a polymerizable functional group show, in general, a glass transition temperature below room temperature, therefore, have had limited applications.
In the course of development of polymers derived from a vinyl ether, the present inventors found that a vinyl ether copolymer having a glass transition temperature above room temperature can be obtained by using a vinyl ether having an alicyclic structure, and made clear that, in particular, a block copolymer obtained by living cationic polymerization shows two or more glass transition temperatures attributed to each block segments (Non-patent Literature 1).                Non-patent Literature 1: The Society of Polymer Science, Japan, Preprint Vol. 54, No. 2, p. 2497        
Therefore, by using a vinyl ether having an alicyclic structure and further using a particular form of polymerization, there may be provided a copolymer having desirable properties in addition to the property of glass transition temperature above room temperature.